The present invention relates to a touch panel device for detecting the touch of a finger or an object, and more specifically relates to a touch panel device using IDTs for detecting such a touch by detecting a cutoff of a surface acoustic wave.
With the spread of computer systems, mainly personal computers, there has been used a device for inputting new information or giving various instructions to a computer system by pointing at a position on a display screen of a display device on which information is displayed by the computer system, with a finger or an object. In order to perform an input operation with respect to the information displayed on the display screen of the display device of a personal computer or the like by a touching method, it is necessary to detect a touched position (indicated position) on the display screen with high accuracy.
Examples of known touch panel devices for detecting the position touched by a finger or an object are classified into: {circle around (1)} a resistance film type; {circle around (2)} an electrostatic capacity type; {circle around (3)} an electromagnetic induction type; and {circle around (4)} an ultrasonic wave type. Although both {circle around (1)} and {circle around (2)} are of types using a light lucent conductive film of, for example, ITO (Indium Tin Oxide), the light lucent conductive film is not perfectly transparent, and therefore these types have a problem in the aspect of brightness because about 20% of the quantity of light is lost when light from a liquid crystal display surface passes through a touch panel unit. Besides, in the case where a touch panel device of such a type is employed in a reflective type liquid crystal display device, since light passes through the touch panel unit twice, the brightness problem is enhanced. On the other hand, type {circle around (3)} has a difficulty in reducing the size and also has a problem that a special input pen is required.
In contrast, type {circle around (4)} detects a position touched by a finger or an object by propagating a surface acoustic wave (hereinafter also referred to as the xe2x80x9cSAWxe2x80x9d) along a glass plate serving as a non-piezoelectric substrate, for example, and detecting attenuation of the surface acoustic wave caused by the touch of the finger or object on the glass plate (Japanese Patent Application Laid-Open No. 55-153041/1980, etc.). This ultrasonic wave type achieves an excellent transparency and requires no special input pen.
However, in conventional touch panel devices of the ultrasonic wave type, since transducers for generating surface acoustic waves and detecting the same are constructed by ceramic transducers, this type of touch panel devices have problems, such as difficulty in reducing the thickness and size, higher costs of the parts and difficult mounting, in comparison with the touch panel devices of other types. Moreover, it is necessary to provide a reflector along the edge of the glass plate, resulting in high costs on the whole.
Therefore, there has been proposed a type in which an IDT (Inter Digital Transducer: comb-like electrode) capable of being formed collectively using a photolithography technique is used as a transducer (Japanese Patent Applications Laid-Open Nos. 6-43995/1994, 6-75688/1994, 6-75689/1994, 6-149459/1994, 11-21925/1999, etc.). This type allows mass production, thereby achieving a reduction in the costs.
In this touch panel device, a plurality of excitation elements, each composed of an input IDT and a piezoelectric thin film, are provided on one end of the glass plate, and a plurality of receiving elements, each composed of an output IDT and a piezoelectric thin film similarly, are provided on the other end of the glass plate at positions opposite to the excitation elements. Electric signals are inputted to the respective excitation elements to excite the surface acoustic waves and propagate the surface acoustic waves along the glass plate, and the propagated surface acoustic waves are received by the receiving elements. Then, if a finger or an object touches the propagation path of the surface acoustic wave along the glass plate, the surface acoustic wave is attenuated. It is therefore possible to detect whether touching is made and the touched position by detecting whether there is attenuation in the level of the receiving signals of the receiving elements.
FIG. 1 is an illustration showing the structure of such a conventional touch panel device using IDTs. In FIG. 1, numeral 1 is a glass plate, and a plurality of input IDTs 2 for exciting a surface acoustic wave are arranged into a line on one end of each of the X-direction and Y-direction of the glass plate 1 so that the input IDTs 2 correspond to a plurality of tracks, respectively. Moreover, a plurality of output IDTs 3 for receiving the surface acoustic wave are arranged stepwise on the other end of each of the X-direction and Y-direction of the glass plate 1 so that the output IDTs 3 face the input IDTs 2. With such a positional arrangement, the distance between the input IDT2 and output IDT 3 is varied according to each track so as to vary the receiving timing in the respective output IDTs 3, so that a track on which the receiving signal is attenuated can be identified accurately.
In the touch panel device having such a structure, the output IDTs 3 need to be arranged stepwise so as to vary the time from the excitation of the surface acoustic wave to the reception thereof in each track, and therefore problems arise that, a region for providing the input IDTs 2 and output IDTs 3 (hereinafter referred to as the xe2x80x9cframe regionxe2x80x9d) is wide and a region where the touched position is detectable (hereinafter referred to as the xe2x80x9cdetection regionxe2x80x9d) is relatively narrow as shown in FIG. 1. Such problems become severer as the number of tracks is increased, and thus this positional arrangement is not practicable. Hence, there is a demand for the development of a touch panel device which is capable of identifying the respective tracks by a technique different from a technique based on the difference in the propagation time, and capable of arranging not only the input IDTs 2 but also the output IDTs 3 into a line.
It is an object of the present invention to provide a touch panel device capable of arranging both of the input IDTs and output IDTs respectively into a line, narrowing a frame region and widening a detection region.
Another object of the present invention is to provide a touch panel device capable of always accurately detecting a touched position without being affected by a change in a temperature environment.
A touch panel device according to the first aspect is a touch panel device comprising a plurality of input IDTs for exciting surface acoustic waves and a plurality of output IDTs for receiving the surface acoustic waves, correspondingly to a plurality of tracks of a non-piezoelectric substrate, for propagating surface acoustic waves along the non-piezoelectric substrate between the input IDTs and the output IDTs and detecting a position of an object touching the non-piezoelectric substrate based on results of receiving the surface acoustic waves by the output IDTs, wherein each of the plurality of input IDTs has a wideband electrode structure, each of the plurality of output IDTs has a matched filter structure for obtaining an output signal upon receipt of a specific signal sequence, and the specific signal sequence is varied according to each of the plurality of tracks.
In the touch panel device of the first aspect, each input IDT has a wideband electrode structure, and each output IDT has a matched filter structure for obtaining an output upon receipt of a specific signal sequence, so that each output IDT outputs an output signal only when it receives a specific signal sequence set for itself but outputs no output signal upon receipt of other signal sequences. Moreover, since the specific signal sequence is varied according to each of a plurality of tracks, the output IDTs corresponding to a plurality of tracks can never output their output signals simultaneously with respect to a single specific signal sequence. Therefore, even when the input IDTs and output IDTs are respectively arranged into a line, it is possible to detect to which track an output signal is related. Hence, the frame region can be narrowed, and a large detection region can be obtained.
A touch panel device according to the second aspect is based on the first aspect, and comprises: an application unit for generating mutually different specific signal sequences in time series and simultaneously applying the generated time-series signal sequences to a plurality of input IDTs, respectively; and a detection unit for synthesizing output signals of the respective output IDTs and detecting a position of a track touched by the object, based on a result of the synthesis. In the touch panel device of the second aspect, signal sequences obtained by arranging signal sequences matching the respective output IDTs in time series are simultaneously applied to the respective input IDTs, and a touched position is detected based on a synthesized signal of the output signals of the respective output IDTs. It is therefore possible to identify a touched track with a simple structure. Moreover, since the surface acoustics waves from the respective input IDTs are always excited in the same phase, a diffraction problem does not occur, thereby improving the detection accuracy.
A touch panel device according to the third aspect is based on the second aspect, wherein a predetermined time interval is introduced between adjacent signal sequences arranged in time series during application of the time-series signal sequences to the plurality of input IDTs, respectively. In the touch panel device of the third aspect, when arranging a plurality of specific signal sequences matching the respective output IDTs in time series, a predetermined time interval is introduced between adjacent signal sequences. It is therefore possible to clearly distinguish the respective signal sequences and prevent an erroneous operation of signal detection.
A touch panel device according to the fourth aspect is based on any one of the first through third aspect, wherein gate signals are generated according to receiving timings of signal sequences matching the plurality of output IDTs, respectively, to selectively fetch an output signal of each of the plurality of output IDTs by masking. In the touch panel device of the fourth aspect, an output signal of a signal sequence corresponding to each output IDT is selectively fetched by performing masking using a gate signal. It is therefore possible to accurately detect only an output signal of a signal sequence matching an output IDT itself and prevent an erroneous operation of signal detection.
A touch panel device according to the fifth aspect is based on any one of the first through fourth aspects, wherein a plurality of input IDTs and/or a plurality of output IDTs are grouped into a plurality of blocks, and a position touched by the object is detected independently in each block. In the touch panel device of the fifth invention, a plurality of input IDTs and/or a plurality of output IDTs are grouped into blocks, and detection processing is performed independently in each block. Therefore, even when the detection region is wide and the number of tracks is large, it is possible to readily perform the detection.
A touch panel device of the sixth aspect is based on the fifth aspect, wherein a same specific signal sequence is doubly used for different blocks. In the touch panel device of the sixth aspect, the same signal sequence can be used for different blocks. Therefore, even when the detection region is wide and the number of tracks is large, it is possible to set signal sequences effectively.
A touch panel device according to the seventh aspect is based on any one of the first through sixth aspects, and further comprises at least one set of input/output IDTs for detecting a temperature of the non-piezoelectric substrate. In the touch panel device of the seventh aspect, a temperature is detected by at least one set of input/output IDTs provided on the non-piezoelectric substrate. It is therefore possible to perform an accurate detection operation by considering a change in temperature which affects the velocity of a surface acoustic wave.
A touch panel device according to the eighth aspect is based on the seventh aspect, wherein an amplifier is connected to the input/output IDTs for temperature detection so as to construct a surface acoustic wave oscillator, and temperature compensation is performed using an oscillation signal of the surface acoustic wave oscillator. In the touch panel device of the eighth aspect, temperature compensation is performed using an oscillation signal of the surface acoustic wave oscillator for oscillating a surface acoustic wave according to a temperature. It is therefore possible to carry out temperature compensation in real time and perform an accurate detection operation.
A touch panel device according to the ninth aspect is based on the eighth aspect, wherein the input/output IDTs for temperature detection have a fundamental period identical with a fundamental period of the input IDT and output IDT for position detection, synthesize an oscillation signal and the specific signal sequences, and apply the resultant synthesized signal to the input IDT for position detection. In the touch panel device of the ninth aspect, a synthesized signal obtained by synthesizing an oscillation signal of the surface acoustic wave oscillator and the specific signal sequences is applied to the input IDT for position detection. It is therefore possible to automatically compensate for a change in temperature.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.